This invention relates generally to a filter bag of the type used to separate particulate matter from a gas stream and more particularly to a filter bag which can be releasably attached and sealed to a cap without the use of separate external clamping elements. One example of the use of such filter bags is in bag houses used in steel mills, cement and limestone plants and the like, where gas-borne particulate matter generated in the manufacturing processes must be separated. Thousands of bags may be used in an industrial installation, and though denominated "bags," these filters are frequently sleeves of extended length, open at both ends. Generally, gas-bearing particulate matter enters a hopper having a tube sheet for its top. The tube sheet is filled with holes, each hole having a collar to which one open end of the filter bag is attached by means of a conventional hose clamp. The tubes extend vertically upward and are attached at the other end to a termination cap which is suspended from a support. Gas leaves the hopper through the tube sheet and passes upward through the filter bag and outward through the wall of the filter bag, leaving behind the particulate matter, which falls back toward the hopper. The cap termination supporting member may be connected to a vibrator which is periodically activated to free particulate matter from the pores of the filter bag. At intervals, the filter bags are replaced in what heretofore has been a labor-consuming effort.
In order to save labor in filtering applications, it is desired that the filter bag be releasably joined to the cap in the simplest and most efficient manner. However, to prevent leakage of particulate matter around the joint between cap and filter bag, it is necessary that a tight seal be provided. Further, the longitudinal forces exerted on the filter bag from the gases discharging against the cap operate to longitudinally separate the filter from the cap unless interference or high friction means or both are provided to prevent such separation. Thus, a desire for simplicity and speed in installing and removing filter bags is compromised by the necessity for prevention of leakage of particulate matter and complete separation of the filter bag from the cap.
As a result, the cap generally includes a radially extending circular flange or rim which is inserted into an open end of the filter bag. A steel band is then tightened around the bag, pressing the bag against the cap in the manner of a hose clamp. The steel band, approximately one-half inch wide, prevents the bag from being pulled over the radial flange or rim. In other applications, only a spring is used in clamping the bag against the cap periphery to provide attachment and sealing. However, as the filter becomes clogged with particulate matter, longitudinal forces build up within the bag which tend to pull the bag from the cap. Thus, the former method requires external clamping elements and time-consuming labor, whereas the later approach is simple but ineffective without further attachment means for holding and sealing the bag to the cap.
What is needed is a filter bag which is quickly and easily attached to the cap without need for external members and provides an effective joint and seal.